Pumps froth-handling

Vertical slurry pumps are particularly popular in froth handling circuits. To handle the combination of soUds, air, and liquids, a double suction impeller is often recom-... 

A very common misunderstanding in the industry is that the flow rate of slurry must be multiplied by the froth factor to size the pump. This violates a very fundamental prin ciple that gases or air are compressible fluids. In other words, as the bubbles pass through the impeller they are compressed and reduced in size. In fact, the proper sizing of slurry pumps to handle froth must be based on a full examination of the system. For example, if... 

Example. Consider the observed properties of bituminous froth produced in the oil sands hot water flotation process. When fresh, the froth is very viscous when stagnant (hard to pump) but becomes less viscous (twice as easy to pump) when it is flowing. As it is handled, or stored, the entrained air is released and it becomes less viscous (eventually six times as easy to pump). 

You have a pump that was designed to handle fresh, flowing froth at a process temperature of 80 °C, but there is a process interruption and the pump is halted for two days, during which time the whole circuit cools to the treatment plant s ambient temperature of about 20 °C. What will happen when you eventually try to restart the pump ... 

Using this concept of froth factor to size pumps must be done veiy carefully. Different grades of froth leads to different levels of entrained gases, as shown in Table 8-15. Con ventional centrifugal pumps can not handle excessive amounts of entrained gases. 

Special pumps are available for handling froth and entrained gases. One interesting design is the Sulzer-Ahlstrom ART pump. It features holes through the impeller leading... 

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